X-ray computed tomography apparatuses require high-speed X-ray ON/OFF control and high-speed X-ray modulation. The high-speed X-ray ON/OFF control and high-speed X-ray modulation can be realized by controlling a bias voltage to be applied to a bias electrode in an X-ray tube.
An anode in the X-ray tube rotates typically at a rotational frequency of about 50 to 200 Hz, that is, in a rotation period of about 5 to 20 msec. When high-speed X-ray ON/OFF control or high-speed X-ray modulation is executed in this rotation period, the X-ray intensity is switched several to several ten times while the anode rotates once. For example, when a multiple of the X-ray ON/OFF switching period coincides with the rotation period of the anode, electron beams bombard only limited portions of the anode. Temperature nonuniformity is therefore generated on the anode, and there is a fear of local partial damage to the anode at only the limited portions. The partial damage causes anode roughening and may cause discharge or nonuniformity of the X-ray dose.
It is an object of embodiments to provide an X-ray computed tomography apparatus, high voltage generation device, and radiological image diagnostic apparatus capable of reducing partial damage to the anode.